This invention relates to apparatus and methods for reading the concentration of a medically significant component of a biological fluid from a test strip. It is disclosed in the context of an apparatus and a method for reading the concentration of glucose in blood reacted on a test strip with a chemistry with which the strip has previously been treated.
The difficulty many people have with preparing test strips treated with chemistries with bodily fluids such as blood and urine is known. Many users of such strips have poor eyesight owing to diabetes, to age, and to other causes as well. Many users have reduced dexterity or strength in their hands owing to age and to other causes. Frequently these causes are the reasons why these users are testing their bodily fluids for, for example, glucose concentration to begin with.
The problems with such strips only begin with dosing the strips with the bodily fluid or fluids to be analyzed. The chemistries are reactants with the medically significant component(s) of the fluids. These reactants react with the medically significant component(s) resulting typically in some colorimetric indication of the concentration of the medically significant component of the fluid. However, these reactions continue, typically for extended times, until all of the reactants have reacted. Consequently, it is generally necessary to time the reaction of the medically significant component with the strip chemistry so that a colorimetric comparison of the reacted strip chemistry to a standard on a color chart can be made at some established time after the reaction is initiated by depositing the fluid on the strip. Otherwise, if the reaction is not permitted to proceed long enough, or is permitted to proceed too long, the color corresponding to the extent of the reaction will not match the correct standard on the chart.
In addition to potential problems with how long the chemistry on the strip and the medically significant component of the body fluid are permitted to react, there are problems with many of such chemistry systems with how much of the body fluid is applied to the strip, since incorrect amounts of the reactants may affect the validity of the test as adversely as errors in the timing of the reaction. Either way, a false reading, sometimes with dire consequences, will result.
The present invention makes use of an endpoint chemistry system of the type described in U.S. Pat. No. 4,929,545. The disclosure of U.S. Pat. No. 4,929,545 is incorporated herein by reference. The advantages of an endpoint chemistry are clear. For the user who frequently has poor eyesight and/or manual dexterity, there is no need to be concerned about how long the reaction has proceeded. The reaction reaches an endpoint in relatively short order after which there is no significant shift in the color of the reaction products on the strip. In addition, the architecture of the strip described in U.S. Ser. No. 07/661,788, filed Feb. 27, 1991, IMPROVED TEST STRIP, naming as inventors McCroskey, Freitag, Smith, Dean, Secrest and Bouse, and assigned to Boehringer Mannheim Corporation, is such that the proper dose of the body fluid, the biologically significant component of which is to be reacted with the chemistry on the strip, will always be available for the reaction. Any excess is wicked away from the reaction site by the strip architecture. Thus, all the user need do is be sure enough of the bodily fluid is present at the reaction site on the strip to react with the chemistry with which the strip is treated. The disclosure of U.S. Ser. No. 07/661,788 is incorporated herein by reference.